The present invention relates to a system and method of fuel cell power generation, in which electric power is generated by using a fuel cell.
According to prior art, such system or method of fuel cell power generation as shown in e.g. FIG. 20 and described in Japanese Laid-open Patent Publication Hei 3-257762 was employed. Referring thereto, it comprises: a fuel cell 1; a desulfurizer 3 for removing sulfur content from a source gas such as natural gas; a fuel gas generator 2 for generating a hydrogen-rich gas from the desulfurized source gas, having a reactor 2a therefor and a burner 2b to heat the reactor 2a; and a nitrogen equipment 5 connected to a position upstream of the fuel gas generator 2 by a nitrogen supply pipe 7 having a shut-off valve 6. The fuel generated by the fuel generator 2 is supplied to a fuel electrode 1a of the fuel cell 1 via a reformed gas supply pipe 8, while the residual fuel is supplied to the burner 2b via a hydrogen exhausting connection pipe 9. To an oxidant electrode of the fuel cell, air is supplied by a blower 4.
When power generation is to be stopped according to general systems or methods of fuel cell power generation, supply of a source gas is firstly stopped. The phenomena occurring then can be described as follows with reference to FIG. 20. In a flow channel from the fuel gas generator 2 to the hydrogen exhausting connection pipe 9 via the reformed gas supply pipe 8 and the fuel cell 1, a hydrogen-rich gas is retained particularly in the flow channel from the fuel electrode 1a to the hydrogen exhausting connection pipe 9. Accordingly, there is a fear in such system that when air flows into the hydrogen-rich gas flow channel, due to free convection, from the burner 2b released to atmosphere, the hydrogen may explode.
To solve this problem, when the power generation is to be stopped according to the system or method of fuel cell power generation as described in above described Japanese Laid-open Patent Publication Hei 3-257762 and shown in FIG. 20, the shut-off valve 6 is opened, and nitrogen gas, as an inert gas, is injected, from the nitrogen equipment 5 and then via the nitrogen supply pipe 7, into the gas flow channel from the fuel gas generator 2 to the hydrogen exhausting connection pipe 9 via the reformed gas supply pipe 8 and the fuel cell 1, particularly to the gas flow channel from the fuel electrode 1a to the hydrogen gas exhausting connection pipe 9. Thereby, the hydrogen-rich gas is exhausted, namely purged, from such fuel gas flow channel by the nitrogen gas. The purged hydrogen-rich gas is then burned by the burner 2b. According to conventional systems in such manner, hydrogen explosion is prevented, before it happens, by the purging process of purging the hydrogen-rich gas from the fuel gas flow channel by the nitrogen gas, whereby safety is secured.
A drawback in the conventional systems or methods of fuel cell power generation is that a nitrogen equipment, such as a nitrogen cylinder, is needed for above described purging process by the nitrogen gas. Thus, when it is used for distributed power generation of stationary type for domestic use or for power sources for electric vehicles, there are such problems that a large space and a high initial cost are needed. Other problems are that it needs periodical replacement or replenishment of the nitrogen cylinder as well as high running costs.
Furthermore, at start-up or initial stage of the operation of the fuel gas generator, highly dense carbon monoxide is contained in the generated fuel gas. In the case that the fuel cell is of a solid polymer electrolyte fuel cell, the carbon monoxide poisons a catalyst of the fuel electrode of the fuel cell. However, according to the conventional systems or methods of fuel cell power generation, such fuel gas as containing highly dense carbon monoxide is supplied to the fuel cell, so that the performance of the fuel cell is likely to get deteriorated due to the poisoning of the catalyst of the fuel electrode.